The invention relates generally to what can be broadly categorized as "image writing." The invention's primary intended application for image writing would be as a microlithography printer for semiconductor manufacture; however this field may also include applications such as document printing, photographic reproduction, etc.
The following references are hereby incorporated by reference in their entirety for all purposes:
Ref. 1: "Microlens Scanner for Microlithography and Wide-Field Confocal Microscopy" (U.S. patent application Ser. No. 08/803,096; PCT Serial No. PCT/US97/02949; filed Feb. 20, 1997) PA1 Ref. 2: "Method of Making and an Apparatus for a Flat Diffraction Grating Light Valve" (U.S. Pat. No. 5,661,592, issued Aug. 26, 1997) PA1 Ref. 3: "Flat Diffraction Grating Light Valve" (U.S. Pat. No. 5,841,579, issued Nov. 24, 1998)
Ref. 1 proposed the use of a Digital Micromirror Device (DMD, manufactured by Texas Instruments) as a spatial light modulator for a maskless lithography system. The DMD is manufactured in a megapixel (10.sup.6 pixel) configuration and has a mechanical switching time of 20 microseconds; hence the maximum achievable data rate would be 50.multidot.10.sup.9 bits per sec per DMD unit (i.e. 50 KHz per pixel times 10.sup.6 pixels). Compared to commercial laser writing systems this is a very high rate, but for wafer production applications much higher throughput would be required. Assuming a minimum feature resolution of 0.1 .mu.m, a typical 200-mm wafer can have on the order of 3.multidot.10.sup.12 resolvable feature elements. The wafer design would require a grid snap significantly smaller than the minimum resolvable spot size; hence the number of image data bits per 200-mm wafer would typically exceed 3.multidot.10.sup.13. Commercial lithography steppers achieve throughput levels on the order of 100 wafers per hour, so a competitive maskless lithography system would need to write at least 100.multidot.3.multidot.10.sup.13 image bits per hour, which translates to a data rate of about 1 THz (i.e. 10.sup.12 bits per sec).
One method proposed in Ref. 1 to boost throughput would be to operate several DMD units in parallel, but to achieve a 1 THz pixel rate this would require about 20 megapixel DMD units, each with its own associated optics, servo control, and image generation electronics. A more practical and economical approach to improving throughput would be to use a faster spatial light modulator.